Watching the uncorrupted Nightmare—once a kind guardian—consume the negative apples out of pure desperation and fear changes the vibe of the room. The "Classic" Sans variants see a mirror of their own potential for despair. They see a version of themselves that didn't just lose a timeline, but lost the ability to feel anything but hate. GC Transcript: The Silence After the Storm
"...kid, i've seen some dark resets. but this? this isn't just a bad time. it's a lifetime of them." Sans AUs react to Nightmare AUs | Undertale AUs / GC
"HE WAS JUST PROTECTING THE TREE! WHY WERE THEY SO MEAN TO HIM? HE JUST WANTED TO BE LOVED LIKE DREAM!" GC Transcript: The Silence After the Storm "
This post focuses on the heavy emotional contrast between the standard Sans AUs (the "reactors") and the tragic, twisted nature of Nightmare’s multiverse variants. it's a lifetime of them